Malicious Office (OOXML) — malware analysis report

Static analysis result for SHA-256 6966a2217b89f5db…

MALICIOUS

Office (OOXML)

16.1 KB Created: 2021-05-18 11:57:42 UTC Authoring application: Microsoft Excel 16.0300 First seen: 2021-05-22
MD5: 795bdd99e20cbc0620009cfea7c23237 SHA-1: 493d5a5e51aa15759c5fda016b2866fbc479a183 SHA-256: 6966a2217b89f5db57d0ac0627990bf445588927c39920fdd7965057ec046d0d
168 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1204.002 Malicious File

The VBA macro contains an Auto_Open subroutine that decodes a base64 string and executes it using WScript.Shell. The decoded string is 'aGVsbG8gd29ybGQ=', which is a placeholder and not a functional command. However, the presence of the Auto_Open macro, Shell() call, and WScript.Shell usage strongly indicates an intent to download and execute a secondary payload. The technique of using a base64 encoded string is common for obfuscating malicious commands.

Heuristics 5

  • VBA project inside OOXML medium 4 related findings OOXML_VBA
    Document contains a VBA project — VBA macros present
  • WScript.Shell usage critical OLE_VBA_WSCRIPT
    WScript.Shell usage
    Matched line in script
    cmd = DecodeBase64(cmd)
CreateObject("WScript.Shell").Exec (cmd)
  • CreateObject call high OLE_VBA_CREATEOBJ
    CreateObject call
    Matched line in script
    cmd = DecodeBase64(cmd)
CreateObject("WScript.Shell").Exec (cmd)
  • VBA p-code auto-exec with execution tokens high OLE_VBA_PCODE_AUTOEXEC_EXEC
    Compiled VBA/cache stream contains an auto-execution token together with shell/download/object-execution tokens. This catches p-code-only or source-extraction-failure macro documents where visible source is unavailable.
  • Auto_Open macro low OLE_VBA_AUTO
    Auto_Open macro
    Matched line in script
    Attribute VB_Name = "Module1"
Sub Auto_Open()

Extracted artifacts 2

Files carved from inside the sample during analysis.

FilenameKindSourceSize
macros.bas vba-macro oletools.olevba.extract_macros (decoded VBA source from OOXML) 2403 bytes
SHA-256: 8702d6b1cc324e471bad53710d8093407f7cf1d4316ef2bcca4a8c9184aea86e
Preview script
First 1,000 lines of the extracted script
Attribute VB_Name = "ThisWorkbook"
Attribute VB_Base = "0{00020819-0000-0000-C000-000000000046}"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = True
Attribute VB_TemplateDerived = False
Attribute VB_Customizable = True

Attribute VB_Name = "Sheet1"
Attribute VB_Base = "0{00020820-0000-0000-C000-000000000046}"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = True
Attribute VB_TemplateDerived = False
Attribute VB_Customizable = True

Attribute VB_Name = "Module1"
Sub Auto_Open()


Dim cmd As String

cmd = "aGVsbG8gd29ybGQ="

cmd = DecodeBase64(cmd)
CreateObject("WScript.Shell").Exec (cmd)

End Sub


Function DecodeBase64(b64$)
    Dim b
    With CreateObject("Microsoft.XMLDOM").createElement("b64")
        .DataType = "bin.base64": .Text = b64
        b = .nodeTypedValue
        With CreateObject("ADODB.Stream")
            .Open: .Type = 1: .Write b: .Position = 0: .Type = 2: .Charset = "utf-8"
            DecodeBase64 = .ReadText
            .Close
        End With
    End With
End Function

Attribute VB_Name = "Sheet2"
Attribute VB_Base = "0{00020820-0000-0000-C000-000000000046}"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = True
Attribute VB_TemplateDerived = False
Attribute VB_Customizable = True

Attribute VB_Name = "Sheet3"
Attribute VB_Base = "0{00020820-0000-0000-C000-000000000046}"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = True
Attribute VB_TemplateDerived = False
Attribute VB_Customizable = True

Attribute VB_Name = "Sheet4"
Attribute VB_Base = "0{00020820-0000-0000-C000-000000000046}"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = True
Attribute VB_TemplateDerived = False
Attribute VB_Customizable = True

Attribute VB_Name = "Sheet5"
Attribute VB_Base = "0{00020820-0000-0000-C000-000000000046}"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = True
Attribute VB_TemplateDerived = False
Attribute VB_Customizable = True
vbaProject_00.bin vba-project OOXML VBA project: xl/vbaProject.bin 19968 bytes
SHA-256: e7ca16168ed1a1f2081d248f0e278822c225dbd9d6dbbc42ab6b05af0d559948

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